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Mojtabaei A. The Etiology of Neonatal Hyperbilirubinemia. Research in Medicine 1973; 2 (1 and 2) :54-57
URL: http://pejouhesh.sbmu.ac.ir/article-1-2649-fa.html

Etiology of Physiologic Neonatal Hyperbili­rubinemia. Every newborn infant develop·s hyperbilirubinemia during the first week of life which is called "physiologic". There are several factors responsible for the development of physiologic hyperbilirubinemia, as follows: 
1. Increased bilirubin production, due to a - Increased blood volume.
b - Decreased R.B.C. survival time. 
c - Increased ineffect_ive hematopoiesis. 
d. Increased bilirubin production from non-hemoglobin sources.· 
2 . Hepatic insufficiency in bilirubin uptake 
a - Decreased Y protein in liver cells, or binding of Y protein by other anions. 
3. Hepatic insufficiency in bilirubin conjuga­ gation due to 
a - Decreased UDP glucuronyl trans­
ferase and UDPG dehydrogenase. 
b - Inhibitory effect of maternal steroids 
on the activity of glucuronyl trans­ferase. 
4. Bilirubin reabsorption from intestine (en­tero-hepatic circulation), due to
a - Absence of physiologic bacterial flora 
of the intestine. 
b - Presence of beta glucuronidase in 
the intestine. 
c - Decreased motility of the bowls. 
5. Hepatic circulation
a - Sudden decrease of oxygen supply to 
the liver after birth. 
b - Portal blood flow bypassing liver through partiaily patent ductus venosus.